To get started with the Free Keyword Tool, just enter a keyword or search term into the relevant field. If you want to conduct competitive intelligence research into your competitors' keyword data, you can also enter the URL of a specific webpage to view keyword data for that page. You can also enter your industry and country to see even more accurate results; it's not unusual for the cost-per-click and other metrics to differ widely from one country to another, even for advertisers bidding on the same keywords in the same industry. 
Keyword everywhere is another useful keyword tool. You can install it on either Firefox or Google Chrome. The tool will be able to show you competition data, cost per click, and Google Keyword search volume of multiple websites and keywords. This free extension can help you to save a lot of time. It can assist you to find long-tail phrases including their precise search volume, competition data, and CPC.
Google's AdWords Keyword Planner tool is another common starting point for SEO keyword research. It not only suggests keywords and provides estimated search volume, but also predicts the cost of running paid campaigns for these terms. To determine volume for a particular keyword, be sure to set the Match Type to [Exact] and look under Local Monthly Searches. Remember that these represent total searches. Depending on your ranking and click-through rate, the actual number of visitors you achieve for these keywords will usually be much lower.
1. AdWords Keyword Planner - It's still the standard, although Google keeps making changes that just aren't helpful. I get that they want us to treat closely-related keywords in such a way that we're not creating multiple pages when we should just have one, but I'd appreciate it if they'd still break down the volume for each keyword that makes up a group (or at least list the keywords they're clumping together into a group).
I came across Longtail Pro this morning, downloaded the trial version and was about to buy the $97 program…seems like a good buy. But the more research I’ve done today, it seems the KC score is an absolute must for anyone who is serious about making money with niche sites. I hate to spend the bucks, but hate even more leaving money and possibly niche site success. Any advice?
Google prefers to not share long tail searches in this tool – because the tool is designed for Google Adwords advertisers. If advertisers bid on those long tails – they would have less competition and therefore pay less for the Adword, and therefore Google would make less money e.g. bidding on the term weight loss for girls under 18 is cheaper than weight loss. 
3. Ninja Outreach: Full disclosure this is my own tool, and it is actually an outreach tool, so you may be wondering how it plays into Keyword Research. The fact is there are quite a few data points that NinjaOutreach gets for me that I find useful in keyword research, such as the articles that are ranking for the keyword in Google, their domain authority, their page authority, the number of backlinks they have, and other social and contact data. It's pretty valuable stuff, especially if there is going to be an outreach campaign tied into the keyword research. I wrote a great article with Jake from LTP showing the combination of the two tools.
It would be great if you can provide comparative analysis of this tool with Google Keyword Planner. Since you’re using this tool so you can provide best comparison. One differentiation which I understood is that this tool works for yahoo and bing as well whereas Google keyword planner works only for Google but Google being a dominating search engine, gives the highest returns, so only this reason may not be enough to buy it.